This invention relates to apparatus for plugging tubular members and more specifically relates to a tube plug tip restrainer apparatus for restraining the tip of a tube plug from traveling in a tube when the tip is fracturedly separated from the plug during the process of extracting the plug from the tube.
It is well known that in a nuclear reactor a steam generator generates steam when heat is transferred by conduction through a heat conductor boundary separating a radioactive primary fluid from a secondary fluid, wherein the secondary fluid is water and wherein the radioactive primary fluid obtains a higher temperature than the secondary fluid. As the temperature of the secondary fluid increases, the secondary fluid reaches saturation temperature beyond which saturation temperature increasing fractions of the secondary fluid enter the vapor phase thereby producing steam. The steam generator typically includes a plurality of conduits or tubes therein through which the primary fluid flows. The walls of these tubes function as the heat conductor boundary for conducting heat from the primary fluid to the secondary fluid.
As indicated hereinabove, in a nuclear reactor the primary fluid flowing in the steam generator tubes is radioactive; hence, the steam generator is designed such that the radioactive primary fluid does not radioactively contaminate the secondary fluid by mingling with the secondary fluid. It is therefore desirable that the tubes remain leak-tight so that radioactive primary fluid remains everywhere separated from the secondary fluid to avoid mingling the radioactive primary fluid with the secondary fluid.
Occasionally, due to tube wall defects or tube wall cracking caused by stress and corrosion during operation, the steam generator tubes may develop surface and volume flaws and thus may not remain leak-tight. If through-wall cracking occurs due to the flaws, the radioactive primary fluid may mingle with the secondary fluid. Thus, corrective action may be necessary to ensure that the primary fluid does not mingle with the secondary fluid. Such corrective action may be to plug the tubes having flaws.
After the steam generator tube having the flaws has been plugged, it may be necessary to extract the plug. A tube plug may be extracted, for example, in order to repair the flawed tube or merely to replace a defective plug. One type of tube plug used in nuclear reactor steam generators is generally referred to in the art as a mechanical tube plug. The mechanical tube plug usually includes a tapered bore therein having an expander completely captured in the bore, which expander is used to expand the plug into engagement with the tube wall for sealingly plugging the tube when the expander is pulled downwardly towards the narrower portion of the tapered bore. If it is desired to extract the plug from the tube, the expander typically is pushed upwardly in the bore until the expander impacts the tip of the plug causing fracture and failure of the plug body and causing separation of the tip of the plug from the plug body. Separation of the tip of the plug from the plug body allows space for access of a tungsten inert gas (TIG) welding torch in the bore of the plug. The torch is used to make weld passes around a portion of the bore of the plug thereby shrinking and relaxing the plug by heating the plug to provide easier extraction from the tube. However, if the tip of the plug is unrestrained after separation, the tip may travel upwardly with relatively high velocity after separation from the plug body and may become lodged in or damage the tube. Thus, the tip of the plug and the expander should be restrained during the separation process so that the tip of the plug does not travel upwardly into the tube. Several designs of restrainers have been tried experimentally with limited success.
There are several devices known in the art for plugging tubular members. One such device is disclosed by U.S. Pat. No. 679,393 issued July 30, 1901 in the name of A. L. McPherson and entitled "Plug for Casings of Oil Wells". This patent discloses a plug for plugging the casings of oil wells. The plug, which when lowered to the bottom of the casing, will automatically clamp itself within the casing at the bottom thereof and will thus prevent sand from rising up in the casing through the open lower end of the casing. The plug includes external upwardly-pointing ratchet-teeth. If the plug is moved upwardly in the casing, the upwardly-pointing ratchet-teeth will engage the inner surface of the casing and oppose the upward movement of the plug. Although the McPherson patent may disclose a plug capable of engaging the casing such that the upward movement of the plug is opposed, it does not appear that the McPherson patent discloses a tube plug tip restrainer apparatus for restraining the tip of a tube plug when the tip is fracturedly separated from the plug body during the process of extracting the plug from a tubular member.
Another device for plugging tubular members is disclosed by U.S. Pat. No. 1,050,557 issued Jan. 14, 1913 in the name of H. L. McLaughlin and entitled "Plug for Oil and Gas Wells". The McLaughlin device includes a circular plug support around which is arranged an expansible plug, preferably made of rubber. The plug is suitably longitudinally compressed, thereby expanding so that the periphery of the plug will engage the inner walls of the casing or tubing. Although this patent may disclose an expansible plug capable of being longitudinally compressed, thereby expanding to engage the inner walls of a tube, this patent does not appear to disclose a tube plug tip restrainer as provided by the present invention for restraining the tip of a plug when the tip is fracturedly separated from the plug.
Yet another device for plugging a tube is disclosed by U.S. Pat. No. 4,310,029 issued Jan. 12, 1982 in the name of Matthew Dudek entitled "Expandable Tube Plug". The Dudek device comprises a first solid cylindrical rigid body member having a threaded bore extending axially inwardly from one end thereof; a bolt threadably received in the bore; a tubular sleeve of rubber or other compressible material slidably receiving the bolt and a second rigid body member of tubular configuration. The sleeve is positioned between the first and second body members. Upon the threading of the bolt into the first body member, the compressible sleeve is caused to expand radially outwardly into sealing engagement with the inner wall of a heat exchanger tube and radially inwardly into sealing engagement with the threads of the bolt. In order to remove the plug, the bolt is unscrewed from the cylindrical member sufficiently to relieve the compression of the expandable sleeve. However, the Dudek patent does not appear to disclose a tube plug tip restrainer as provided by the present invention for restraining the tip of a tube plug.
A tube plug having an elastomeric material on the outer surface thereof for enhancing the seal between the tube plug and a heat exchange tube is disclosed by U.S. Pat. No. 4,502,511 issued Mar. 5, 1985 in the name of Paolo R. Zafred entitled "Tube Plug" and assigned to the Westinghouse Electric Corporation. The Zafred device comprises a one-piece mechanical plug having one open end and one closed end, which plug is capable of being inserted in a heat exchange tube and internally expanded into contact with the inside surface of the heat exchange tube. The tube plug further comprises a groove extending around the outside circumference thereof which has an elastomeric material disposed in the groove for enhancing the seal between the tube plug and the tube. Although the Zafred patent may disclose a device, including elastomeric material, for plugging a steam generator tube, the Zafred patent does not appear to disclose the tube plug tip restrainer apparatus as described and claimed herein.
Consequently, while the prior art discloses devices for plugging tubes, the prior art does not appear to disclose a device for restraining the tip of a tube plug from traveling in a tube when the tip is fracturedly separated from the plug during the process of extracting the plug from the tube.
Therefore, what is needed is a tube plug tip restrainer apparatus for restraining the tip of a tube plug from traveling in a tube when the tip is fracturedly separated from the plug during the process of extracting the plug from the tube.